具有寿命参数的特征意味着什么? [英] What does it mean for a trait to have a lifetime parameter?

问题描述

我了解生命周期参数如何应用于函数和结构，但是特征具有生命周期参数意味着什么?是将生命周期参数引入其方法的捷径，还是其他?

I understand how lifetime parameters apply to functions and structs, but what does it mean for a trait to have a lifetime parameter? Is it a shortcut to introduce a lifetime parameter to its methods, or is it something else?

推荐答案

如果您的特征具有生命周期约束，那么该特征的 implementor 可以参与相同的生命周期.具体来说，这使您可以存储具有该生存期的引用.它不是不是的快捷方式，用于指定成员方法的生存期，而那样的方式则使困难和令人困惑的错误消息成为现实！

If you have a trait with a lifetime bound, then implementors of the trait can participate in the same lifetime. Concretely, this allows you to store references with that lifetime. It is not a shortcut for specifying lifetimes on member methods, and difficulty and confusing error messages lie that way!

trait Keeper<'a> {
    fn save(&mut self, v: &'a u8);
    fn restore(&self) -> &'a u8;
}

struct SimpleKeeper<'a> {
    val: &'a u8,
}

impl<'a> Keeper<'a> for SimpleKeeper<'a> {
    fn save(&mut self, v: &'a u8) {
        self.val = v
    }
    fn restore(&self) -> &'a u8 {
        self.val
    }
}

请注意，如何在生命周期中同时对struct和trait进行参数化，并且该生命周期相同.

Note how both the struct and the trait are parameterized on a lifetime, and that lifetime is the same.

SimpleKeeper<'a>的save()和restore()的非特征版本会是什么样?

What would the non-trait versions of save() and restore() look like for SimpleKeeper<'a>?

实际上非常相似.重要的部分是该结构本身存储了引用，因此它需要为内部的值提供一个生命周期参数.

Very similar, actually. The important part is that the struct stores the reference itself, so it needs to have a lifetime parameter for the values inside.

struct SimpleKeeper<'a> {
    val: &'a u8,
}

impl<'a> SimpleKeeper<'a> {
    fn save(&mut self, v: &'a u8) {
        self.val = v
    }
    fn restore(&self) -> &'a u8 {
        self.val
    }
}

它们的含义与特征版本完全一样吗?

And would they mean exactly the same thing as the the trait version?

是的！

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